Why function GetLastError returns 2? - winapi

Question

Today, I decided to practice by creating a simple program that creates a new file. But I got a problem that the file is not being created. How to solve this?
Firstly, I'm importing the required crate, then creating the err() function for printing errors after creating the file, if they will.
Secondly, I'm creating a function to_u16(), because LPCWSTR type needs *const u16.
Thirdly, I'm calling the CreateFileW() function for creating file.rs, and passing all necessary arguments (according to this and this).
createfile.rs
use winapi::shared::minwindef::DWORD;
use winapi::um::winnt;
use std::ffi::CString;
use winapi::um::errhandlingapi;
use winapi::ctypes::*;
use winapi::um::minwinbase::*;
use winapi::um::fileapi;
use std::io;
fn err(){//print the last error
unsafe{
let xui =errhandlingapi::GetLastError();
print!("{:?}",xui) ;// 2
}
}
fn to_u16(s: &str) ->*const u16 {
let c_str = CString::new(s).unwrap();
c_str.as_ptr() as *const u16
}
fn main() {
unsafe{
let name:winnt::LPCWSTR =to_u16("file.rs") ; //lpFileName
let acces:DWORD = winnt::GENERIC_WRITE; //dwDesiredAccess
let share = winnt::FILE_SHARE_DELETE|winnt::FILE_SHARE_READ|winnt::FILE_SHARE_WRITE;//dwShareMode
let security = 0 as *mut SECURITY_ATTRIBUTES ;//lpSecurityAttributes
let disposition = fileapi::OPEN_EXISTING; //dwCreationDisposition
let atr = winnt::FILE_ATTRIBUTE_NORMAL;//dwFlagsAndAttributes
let handle = 0 as *mut c_void;//hTemplateFile
fileapi::CreateFileW(name,acces,share,security,disposition,atr,handle);
err();
}
}
cargo.toml
[package]
name = "createfile"
version = "0.1.0"
edition = "2021"
# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
[dependencies]
kernel32-sys = "0.2.2"
winapi = "0.3.9"
[target.'cfg(windows)'.dependencies]
winapi = { version = "0.3.9", features = ["winuser", "fileapi", "errhandlingapi"] }

Answer 1

Error 2 is ERROR_FILE_NOT_FOUND.
You say you want to create a new file, but you are setting the disposition argument to OPEN_EXISTING, so if file.rs does not already exist then CreateFileW() will fail with this error.
Try using CREATE_ALWAYS, CREATE_NEW, or OPEN_ALWAYS, per the documentation:
[in] dwCreationDisposition
An action to take on a file or device that exists or does not exist.
For devices other than files, this parameter is usually set to OPEN_EXISTING.
For more information, see the Remarks section.
This parameter must be one of the following values, which cannot be combined:
Value
Meaning
CREATE_ALWAYS2
Creates a new file, always.If the specified file exists and is writable, the function overwrites the file, the function succeeds, and last-error code is set to ERROR_ALREADY_EXISTS (183).If the specified file does not exist and is a valid path, a new file is created, the function succeeds, and the last-error code is set to zero.For more information, see the Remarks section of this topic.
CREATE_NEW1
Creates a new file, only if it does not already exist.If the specified file exists, the function fails and the last-error code is set to ERROR_FILE_EXISTS (80).If the specified file does not exist and is a valid path to a writable location, a new file is created.
OPEN_ALWAYS4
Opens a file, always.If the specified file exists, the function succeeds and the last-error code is set to ERROR_ALREADY_EXISTS (183).If the specified file does not exist and is a valid path to a writable location, the function creates a file and the last-error code is set to zero.
OPEN_EXISTING3
Opens a file or device, only if it exists.If the specified file or device does not exist, the function fails and the last-error code is set to ERROR_FILE_NOT_FOUND (2).For more information about devices, see the Remarks section.
TRUNCATE_EXISTING5
Opens a file and truncates it so that its size is zero bytes, only if it exists.If the specified file does not exist, the function fails and the last-error code is set to ERROR_FILE_NOT_FOUND (2).The calling process must open the file with the GENERIC_WRITE bit set as part of the dwDesiredAccess parameter.